1. Field of the Invention
The present invention relates to a transfer apparatus. More particularly, the invention relates to a transfer apparatus for linearly transferring a work such as a substrate in the form of a thin plate.
2. Description of the Related Art
A transfer robot with a mechanism for moving a hand along a linear movement path (linear movement mechanism) has a simpler structure and is less expensive than the so-called articulated robot. Such a transfer robot is often used for carrying in or out a work in the form of a thin plate such as a wafer or a glass substrate with respect to a process chamber in manufacturing a semiconductor fabrication system or a liquid crystal display panel, for example.
An example of such a transfer apparatus for transferring a work in the form of a thin plate is disclosed in JP-A-2005-186259. The disclosed transfer apparatus includes a link arm mechanism as a linear movement mechanism supported by a rotary base. A hand for horizontally holding a work in the form of a plate such as a substrate is mounted to an end of the link arm mechanism. The rotary base is rotatably supported by a stationary base. When the rotary base rotates on the stationary base around a vertical rotation axis, the link arm mechanism rotates correspondingly. The stationary base incorporates a driving source for driving the link arm mechanism and a transmission shaft extending into the rotary base for transmitting the driving force from the driving source to the link arm mechanism. The link arm mechanism includes two links in the form of a parallelogram each including a plurality of arms connected rotatably. The link arm mechanism is driven by the driving force transmitted thereto from the driving source in the stationary base via the transmission shaft. When the link arm mechanism is driven, the work held by the hand moves linearly within a horizontal plane. In this way, the work is transferred from a certain position to another position.
In recent years, the size of a liquid crystal display panel is being increased, and accordingly, the work to be transferred by a transfer apparatus is being increased in size and weight. Further, the movement distance or travel of the hand for holding the work is required to be increased.
However, with the structure of the conventional transfer apparatus, the rigidity of the link arm mechanism needs to be increased to support a work having a large weight, which leads to an increase in weight of the link arm mechanism.
Moreover, to increase the travel of the hand, the length of the arm of the link arm mechanism needs to be increased. When the length of the arm is increased, the position of the link arm mechanism as a whole deviates to be away from the above-described rotation axis. Due to the positional deviation and the increase in weight of the link arm mechanism, a large inertial force is applied to the rotary base in starting or finishing the rotation of the rotary base. As a result, for the rotation, a driving source with a large output needs to be employed, which is not desirable.